Roller-band inertial switch

ABSTRACT

A roller-band inertial switch operable over a predetermined temperature range including a housing; a roller-band cluster disposed within the housing and having a first roller, a second spool-shaped roller and a tension band supporting the rollers within the housing, said band including an oblong orifice adjacent the spool-shape roller and a force-biasing opening adjacent the other roller to bias the cluster adjacent an end wall of the housing; electrical sensing means disposed at the other end wall of the housing to sense movement of the cluster to the other end wall; and a damping fluid in the housing filling the housing at a temperature above the predetermined temperature range and a method for forming the housing.

United States Patent [72] Inventors Fred A. Duimstra;

Douglas 0. Schuler, Albuquerque, N. Mex. [21 Appl. No, 883,736 [22]Filed Dec. 10, 1969 [45] Patented Mar. 2, 1971 [73] Assignee the UnitedStates of America as represented by the United States Atomic EnergyCommission [54] ROLLER-BAND INERTIAL SWITCH 10 Claims, 4 Drawing Figs.

[52] US. Cl 200/61.53, 200/ l 5 3 [51] Int. Cl. ..H0lh 35/14 [50] FieldofSearch ZOO/61.53, 153, 152 (Ball) [5 6] References Cited UNITED STATESPATENTS 3,452,175 6/1969 Wilkes 200/ 153 3,452,309 6/1969 Wilkes3,471,668 10/1969 Wilkes 335/209 ZOO/153 ABSTRACT: A roller-bandinertial switch operable over a predetermined temperature rangeincluding a housing; a roller-band cluster disposed within the housingand having a first roller, a second spool-shaped roller and a tensionband supporting the rollers within the housing, said band including anoblong orifice adjacent the spool-shape roller and a forcebiasingopening adjacent the other roller to bias the cluster adjacent an endwall of the housing; electrical sensing means disposed at the other endwall of the housing to sense movement of the cluster to the other endwall; and a damping fluid in the housing filling the housing at atemperature above the predetermined temperature range and a method forforming the housing.

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DISTANCE INVENTORS' FRED A. DUIMSTRA DOUGLAS O.SCHULER BY msm N010- FIG.3

ROLLER-BAND INERTIAL SWITCH BACKGROUND OF INVENTION Accelerometers andinertial sensing devices are widely used to measure accelerations orother forces resulting from vibrations, changes in speed, or the like.Such accelerometers or inertial sensing devices may include some form ofsensing mass suspended with the system or device so as to be affected bythe acceleration or other force and moved against some sort of sensingmechanism, such as the closure of an electrical switch or contacts.Roller-band devices, such as those described in U.S. Pat. Nos.3,452,175, 3,452,309 and 3,471,668, are particularly adaptable to suchapplications. In these roller-band devices, the rollers in theroller-band cluster form the desired sensing mass. The tension-band ofthe roller-band cluster suspends and constrains the rollers within anappropriate guideway so as to provide virtually frictionless movement ofthe roller-band cluster along the guideway. These roller-band devicesthus are capable of sensing accelerations or other forces with a highdegree of accuracy due to the low and predictable inherent frictionlosses.

In many of theseaccelerations or other force sensing applications, it isdesirable that the sensing mass be restrained by some type of dampingmeans, such as a damping fluid, to provide a measurement of force perunit time, e.g., g-seconds. Since the viscosity of damping fluidsmayvary with changing temperature, such devices are-inherently limited asto'accuracy over any significant temperature range. For example, theviscosity of a typical damping fluid such as silicon oil, may vary asmuch as 500 percent over the temperature range of from about 65 to +160F. A g-second product for a conventional device to operate over thisrange with such a silicon oil damping fluid may vary by :30 percent ormore.

SUMMARY OF INVENTION In view of the limitations of the prior art asnoted above, it is an object of this invention to provide a roller-bandinertial switch which is operable accurately over a predeterminedtemperature range.

It is a further object of this invention to provide an inertial switchof simple construction and design.

Various other objects and advantages will appear from the followingdescription of an embodiment of the invention, and the most novelfeatures will be particularly pointed out hereinafter in connection withthe appended claims. It will be understood that various changes in thedetails, materials and arrangements of the parts, which have been hereindescribed and illustrated in order to explain the nature of theinvention, may be made by those skilled in the art.

The invention comprises a roller-band device including a housing havingguideway walls, sidewalls and end walls; a roller-band cluster disposedwithin said housing, said rollerband cluster having a first roller, asecond spool-shaped roller and a tension-band supporting and restrainingthe rollers within said housing, said band including an'oblong orificeadjacent the spool-shaped roller and a force biasing opening adjacentthe first roller to bias the roller-band cluster adjacent one of the endwalls; electrical sensing means disposed at the other end wall forsensing movement of the roller-band cluster to the other end wall; and adamping fluid in the housing filling the housing at a temperature abovea desired operating temperature range.

DESCRIPTION OF DRAWING DETAILED DESCRIPTION The roller-band inertialswitch or accelerometer of this invention, as illustrated in FIGS. 1 and2, includes a roller-band cluster disposed within a suitable casing orhousing 12. Roller-band cluster 10 includes a first roller or rotatablemember 14 a second rotatable member 16 anda tension band 18.Tension-band 18 may include certain cutouts or openings and be attachedto housing 12 as described in detail below.

The dimensions and density of rotatable member 14 may be selected toprovide the desired coaction between tension-band 18 and roller-bandcluster 10. Rotatable member 16, however, is formed in a spoollike shapeas illustrated having outer rim or ridge supporting portions 15interconnected by a pin or spindle 17. Spindle 17 preferably issufficiently smaller in dimension compared to rim portion 15 to providea passageway 19 of sufficient size to minimize impediment of flow offluid between spindle 17 and tension-band 18.

Housing 12 may include generally parallel oppositely disposed guidewaywalls '20 and 22, sidewalls 24 and 26, and end walls or end caps 28-and30 forming an enclosed, sealed cavity 31. Guideway walls 20 and 22 andsidewalls 24 and 26 may be made as a unitary structure and formed from atubular or the like stock as described below. Sidewalls 24 and 26 may beformed with suitable beveled corners, as shown in FIG. 2, to providenarrow side gaps or passageways and 27 along the sides of roller-bandcluster 10 for passage of fluid thereabout. Side gaps 25 and 27 may bemaintained as small as possible relative to dimensions of a dampingfluid orifice in tension-band 18 (e.g., orifice 58). End walls 28 and 30may include flange or shoulder portions 32 and 34 about three sidesthereof to overlappingly and sealingly engage and abut against theguideway and sidewalls of housing 12. As shown, tensionband 18 may bepassed between the remaining fourth side of end walls 28 and 30 and theadjacent guideway wall 20m 22 and fastened by suitable tabs orextensions on the band. It should be noted, that the ends oftension-band 18 are clamped or fastened to diagonally opposite ends'ofthe guideway wall and are threaded in a generally S-shaped fashion aboutthe rollers 14 and 16 so as to constrain and support the rollers in astable roller-band cluster. End walls 28 and 30 each include a boss 35and 37 fitting into the casing and may also be provided with a suitableraised or thickened portion36 and 38 respec tively to provide clearancefor electrical connections. End walls 28 and 30 may be attached toguideway walls 20 and 22 and sidewalls 24 and26 by anyappropriate'nonconductive adhesive such as certain epoxies which includethickening agents to minimize wicking and which is compatible with theenvironment which the device is to be subjected and with the damping Endwall 28, which is located at the reset end of housing 12 may be providedwith a resilient shock-absorbing pad 40 to prevent any damage to endwall 28 from reset of the rollerband cluster 10. Pad 40 may be made ofany suitable materials such as nitrile rubber epoxy or certain syntheticresilient materials. End wall 38 may also be provided with an initiallyopen fill tube 42 which may be used to fill the cavity of housing 12with the desired damping fluid. Tubing 42 may be made of any appropriatematerial which will seal .to the material of end wall 28, such ascertain alloys of iron, nickel and cobalt.

End wall 30, which may be designated as at'the actuate end of theroller-band device, may be provided with a pair of electrical pins orcontacts 44 and 46. Pin 44 may be passed through an opening 48 into thecavity of housing 12 and terminate with an appropriately shaped contactmember 50. Contact member50 may include any suitable bifurcatedcontacting surfaces or the like which will make positive electricalcontact with tension-band 18 when the roller-band cluster reaches theactuate end of the device. Pin 46 may be suitably supported by end wall30 such as by opening 52. Pin 46 may make contact with'an appropriatelyshaped portion of tensionband 18 such as to tab 54. Tab 54 may bemaintained in electrical contact with pin 46 by an appropriateconductive washer 56 and any conductive cement or adhesive, as deemednecessary. Pins 44 and 46 may be made of any appropriate material whichwill seal to openings 48 and 52 or they may be sealed therewith bysuitable adhesives or sealants.

As shown in FIG. 3, tension-band 18 may include an orifice 58 formetering damping fluid and a suitably shaped force biasing opening 60for biasing the roller-band cluster to the reset end of housing 12.Orifice 58 may be of any suitable shape or of suitable size, dependingon the desired rate of damping fluid metering. It has beenfound, that itis preferable that orifice 58 be generally oval, elliptic or oblong inshape, with generally V-shape ends and the narrow dimension transverseto the direction of tension-band flecture, to minimize any deformationof the tension-band .as it bends around the curvature of the rollers andprevent generation of undesirable force functions. Likewise, it has beenfound that force biasing opening 60 should not include any abrupt orsudden changes in size to prevent the same distortion of thetension-band. Opening 60 may be located along tension-band 18 so as tobe adjacent the contact zone or line'of roller 14 with guideway wallwithout the movement of roller-band cluster 10. The length anddimensions of opening 60 may be chosen to provide a force function asshown in FIG. 4, where the useable portion of the force bias or forcefunction 62 is between vertical lines 64 and 66; the portion of theforcefunction shown by dotted line 68 results from the flecture of contactmember 50. Tension-band 18 may also be provided with suitable lateralprojections or tabs 70 and 72 at opposite ends thereof with dimensionswider than the guideway opening which abut against diagonally oppositeends at outer surfaces of the casing to insure locking of theroller-band cluster in a stable and repeatable condition and preventloosening of this condition. Tab 54 may be provided with a slot 74 andopening 76 to permit connection to pin 46. Opening 76 may include one ormore ears or other sharp protuberances 78 which may partially score pin46 upon contact therewith and insure good electrical connections.

Cavity 31 of housing 12, may be filled with an appropriate damping fluid79 which has a desired viscosity at the temperatures which the device isto be used. A suitable damping fluid may be a silicon oil, such asilicon oil having a viscosity of about .65 centistoke. The dampingfluid preferably fills cavity 31 to a sufficient degree or level toprovide a bubble 80 within the cavity at all temperatures withinthedesired operating range.

Since electrical contact or circuit closure between pins 44 and 46 ismade by electrical contact through contact member 50 and tension-band18, it is desirable that the housing members be made of a nonconductingmaterial. A particularly suitable material for this application isglass. The various housing members may be made by any appropriate means,however, it has been found particularly suitable to form the end walls28 and 30 from glass powders which may be pressed and then sintered atan appropriate temperature to provide a unitary, high strength members.Guideway walls 20 and 22 and sidewalls 24 and 26 may be made from asingle glass tube formed by heating the glass tube as it is disposedabout a mandrel having dimensions slightly less than the desiredinternal dimensions of housing 12 and then evacuating the interior ofthe glass tube. The glass tube may be heated by heating at one end ofthe mandrel and then moving the heat along the tube as the tube issoftened and deformed about the mandrel. The mandrels dimensions may beselected so that when it is heated to this temperature, it expands tothe desired dimensions of housing 12. After the housing guideway walland sidewalls have been formed about the mandrel the heat may be turnedoff and the tube and mandrel cooled. As the mandrel cools it shrinks toits original size permitting removal of the finished housing walls. Themandrel may be made of sufficient length to permit forming of a tubehaving dimensions longer than required for one housing and the finishedhousing walls then cut to desired length.

The roller-band device may be assembled by threading tension-band 18about rollers 14 and 16'and inserting the same within the housingguideway and sidewalls with tabs 70 and 72 extending therebeyond. Asuitable adhesive may be applied as a continuous head around thejuncture of end caps 28 and 30 with the guideway and sidewalls and theend caps disposed in their appropriate position. Tab 54 may be bent overend 30 and slid over pin 46 with opening 76 and ears 78 in contacttherewith. Washer 56 may then be threaded over pin 46 and pressedagainst tab 54 and adhered thereto. The seal of housing 12 may now bechecked by pressurization through fill tube 42 by appropriatepressurized gas. If housing 12 is leak tight, it may be immersedentirely within a reservoir of damping fluid. The damping fluid may bedegassed to insure complete filling of cavity 31. The damping fluid maythen be heated to a temperature above the desired temperature operatingrange for the device while keeping housing 12 immersed therein. When thesystem has reached equilibrium, fill tube 42 may be clamped or pinchedoff and the now filled housing removed from the damping fluid. Aftercleaning of the exterior of housing 12, the end of fill tube 42 may becovered by a bead adhesive to insure complete sealing thereof. As thefinished housing is cooled to the operating temperatures, a vapor orvacuum bubble 80 will be formed therein.

In operation, if the roller-band device, is subjected to someacceleration in the direction of arrow in FIG. 1 or to a force in theopposite direction which is sufficient to overcome the force biasproduced by opening 60 in tension-band 18, the roller-band cluster 10may roll along guideway walls 20 and 22 towards contact member 50. Asthe roller-band cluster 10 rolls along the guideway walls, damping fluid79 may be me tered through orifice 58 and about the ends of rollers 14and 16 along sidewalls 24 and 26 and through side gaps 25 and 27. If theacceleration or force continues for a sufficient period of timedepending on viscosity of the damping fluid and the sizes of opening 58and the sidewall gaps, the roller-band cluster may contact member 50 andcomplete the circuit between pins 44 and 46, as shown by the dottedline. The flow through the orifice 58 and the flow through the sidepassages or gaps 25 and 27 each contribute to the total g-second productcontained. The metering rate of orifice 58 may be substantially constantover the temperature range due to the turbulent-type flow of dampingfluid therethrough. As the temperature varies over the temperaturerange, the size of bubble 80 may change, increasing with decreasingtemperature. When the device is subjected to an acceleration of force asdescribed above, the bubble 80 will be transferred to the reset end ofhousing 12. At the lower temperatures, due to the larger size of bubble80, the rollers will get a head start towards the actuate end andovercome any inconsistencies caused by the laminar flow around the sidepassages or sidewall gap. The orifice 58 and the bubble 80 thus coact toprovide a constant g-second product over the operating temperaturerange.

Bubble 80 may also perform a safing function, in that since the housing12 is filled with damping fluid at a temperature above the temperaturerange, no damage to the housing may occur with excessive temperaturesfrom internal pressures until the temperature is increased above thefilled temperature.

The g-second product for a typical roller-band device of FIGS. 1 through3 may vary with increased g-level. The gsecond product may vary lessthan :10 percent over the temperature range of from about 65 F to +l60F. For such an operating temperature range, cavity 31 of housing 12 maybe filled with damping fluid at a temperature of about F. The filledtemperature may be any temperature above the temperature range and mayexceed the highest temperature of the range by any amount within thestructural limits of the materials of the device, the desired g-secondproduct being monitored and any desired safing level.

These devices may be readily manufactured in miniaturized form. Forexample, the device of FIG. 1 may be about .780 inches long and about.385 inches square with rollers having an outside diameter of about .180inches. Orifice 58 may have an area of about .008 square inches comparedto a total side gap 25 and 27 area of about .0009 square inches. Suchdevices may be used to sense forces of less than 60 to about 1000 gswith g-second products of, for example, from about .7 to about 3.4g-seconds.

We claim:

l. A roller-band inertial switch operable over a desired temperaturerange comprising a tubular casing having a pair of guideway walls spacedapart by sidewalls; a tension-band having adjacent one end thereof alateral projection abutting against an end of said casing and a portionextending along one of said guideway walls an and having adjacentanother end thereof a lateral projection abutting against an oppositeend of said casing and a portion extending along the other of saidguideway walls; a roller-band cluster including a first roller and aspool-shaped roller partially encompassed by said band in generallyS-shaped fashion, said band having an oval orifice adjacent saidspool-shaped roller and a force-biasing aperture adjacent said firstroller and a portion of the guideway wall, ends of said orifice and saidaperture being generally V-shape;

end caps at the ends of said casing each having a boss fitting into thecasing with an edge holding the band against the inner surface of theguideway and having shoulder portions abutting against ends of thecasing to position the end caps; and a damping fluid in said casingfilling said casing at a desired temperature above said temperaturerange.

2. The switch of claim 1 wherein said damping fluid fills a variableportion of said casing over said temperature range.

3. The switch of claim 1 wherein said filling temperature is about 180F. and said temperature range is from about 65 to F. v I

4. The switch of claim 1 wherein said force-biasing aperture biases saidroller-band cluster adjacent one of said end caps and said other end capcarries electrical contact means for sensing movement of saidroller-band cluster to said other end cap.

5. The switch of claim 4 wherein said other end cap carries anelectrical pin projecting from said casing and said band includes anextension disposed about said other end cap, said extension including anaperture disposed about and in contact with said pin.

6. The switch of claim 5 wherein said electrical contact means includesa contact member disposed within said casing and supported by anelectrical pin carried by said other end cap and projecting from saidcasing.

7. The switch of claim 4 wherein said one end cap carries a fill tubefor inserting said damping fluid in said casing.

8. The switch of claim 1 wherein said casing is of glass and said endcaps are of sintered powdered glass.

9. The switch of claim 1 wherein said sidewalls are spaced from saidroller-band cluster a distance to define a passageway having an areasubstantially smaller than the area of said oval orifice.

10. The switch of claim 1 wherein said spool-shaped roller includes apair of rims interconnected by a spindle, the spindle having a diametersubstantially less than the rim diameter.

1. A roller-band inertial switch operable over a desired temperaturerange comprising a tubular casing having a pair of guideway walls spacedapart by sidewalls; a tension-band having adjacent one end thereof alateral projection abutting against an end of said casing and a portionextending along one of said guideway walls an and having adjacentanother end thereof a lateral projection abutting against an oppositeend of said casing and a portion extending along the other of saidguideway walls; a roller-band cluster including a first roller and aspool-shaped roller partially encompassed by said band in generallyS-shaped fashion, said band having an oval orifice adjacent saidspool-shaped roller and a force-biasing aperture adjacent said firstroller and a portion of the guideway wall, ends of said orifice and saidaperture being generally V-shape; end caps at the ends of said casingeach having a boss fitting into the casing with an edge holding the bandagainst the inner surface of the guideway and having shoulder portionsabutting against ends of the casing to position the end caps; and adamping fluid in said casing filling said casing at a desiredtemperature above said temperature range.
 2. The switch of claim 1wherein said damping fluid fills a variable portion of said casing oversaid temperature range.
 3. The switch of claim 1 wherein said fillingtemperature is about 180* F. and said temperature range is from about-65* to +160* F.
 4. The switch oF claim 1 wherein said force-biasingaperture biases said roller-band cluster adjacent one of said end capsand said other end cap carries electrical contact means for sensingmovement of said roller-band cluster to said other end cap.
 5. Theswitch of claim 4 wherein said other end cap carries an electrical pinprojecting from said casing and said band includes an extension disposedabout said other end cap, said extension including an aperture disposedabout and in contact with said pin.
 6. The switch of claim 5 whereinsaid electrical contact means includes a contact member disposed withinsaid casing and supported by an electrical pin carried by said other endcap and projecting from said casing.
 7. The switch of claim 4 whereinsaid one end cap carries a fill tube for inserting said damping fluid insaid casing.
 8. The switch of claim 1 wherein said casing is of glassand said end caps are of sintered powdered glass.
 9. The switch of claim1 wherein said sidewalls are spaced from said roller-band cluster adistance to define a passageway having an area substantially smallerthan the area of said oval orifice.
 10. The switch of claim 1 whereinsaid spool-shaped roller includes a pair of rims interconnected by aspindle, the spindle having a diameter substantially less than the rimdiameter.